Nadia ate 2 slices of pizza. Luis ate 4 slices. If Nadia ate $\dfrac{2}{9}$ of the pizza, what fraction of the pizza is remaining?
If 2 slices represent $\dfrac{2}{9}$ of the pizza, there must have been a total of 9 slices. $\text{fraction of pizza remaining} = \dfrac{\text{number of slices remaining}}{\text{number of slices total}}$ Together they ate 6 slices, which leaves 3 out of 9 slices remaining. There is $\dfrac{3}{9}$ of the pizza remaining.